Temperature and Battery Life
Lithium ion battery life is adversely affected by temperature extremes. High temperatures cause irreversible damage to lithium ion batteries; this damage can be caused during charging or by high outside temperatures. A fully charged battery stored at 40o C (104o F) for a year will have lost 35% of its original storage capacity. The same battery stored at 0o C (32o F) loses only 6% of its capacity. The takeaway message here is that you should store your electric bicycle in as cool conditions as possible. This may mean taking your bicycle indoors in the summer (always a good idea with expensive bikes, anyway), or storing it in a cooler area. Another source of damage is heat from charging, which is most serious in batteries containing carbon anodes. Be careful not to overcharge batteries (such as by leaving them to charge overnight), as the resulting combination of high temperature and charge is very damaging.
The second most important bit of advice for lithium battery care is to avoid storage with a full charge. The recommended charge during storage is just 40%. A 40% charged battery stored in 40o C temperatures loses only 15% of its charge in a year, compared to 35% for a fully charged battery. Only charge your battery before you intend to use it, and never store it with a full charge. Conversely, the batteries should not be stored with very low charge, as this too can erode battery capacity. Ideally, the battery should be stored at cool temperatures with about a 40% charge (or just under half, if your gauge isn't too accurate).
One important caveat to the storage temperature: lithium batteries do not operate well when cold. The battery capacity will be temporarily lowered when the battery is very cold, so warm it up before use. This loss in storage capacity is only temporary, however.
Some of the storage loss can be averted by fully charging and discharging the battery at least once each month. With proper care, you should be able to get up to 3 years of good use out of the battery.